Drum brakes with floating jaws



Feb. 4, 1969 J, u 3,425,521

DRUM BRAKES WITH FLOATING JAWS Filed Jan. 4, 1967 Sheet of 3 LWET Q N I TIIIIIIII'I (/54/1/ Maya/c5 Feb. 4, 1969 J.'MAURICE 3,425,521

DRUM BRAKES WITH FLOATING JAWS Filed Jan. 4, 1967 Sheet L of 5 FIG.3

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J. MAURICE DRUM BRAKES WITH FLOATING JAWS Feb. 4, 1969 Sheet Filed Jan. 4, 1967 FIGS dew/v Mame/c5 United States Patent US. Cl. 188-79.5 Int. Cl. F16d 51/14, 65/56 14 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a drum-brake having two brakejaws mounted floating with respect to the drum, in which there are interposed between the oppositely-facing extremities of the brake-jaws: an operating cylinder containing two sliding pistons, each bearing against one of the jaws through the intermediary of a coupling rod; and a device for automatically taking-up play due to wear of the friction linings mounted on the brake-jaws, said take-up device being mounted diametrically opposite to the operating cylinder with respect to the axis of the drum, and being of the unidirectional type with step-by-step operation, driven in rotation by an actuating lever which is carried on one of said brake-jaws through an articulated coupling, and is coupled to the operating cylinder by an abutment rod parallel to the coupling rod of the brake-jaw considered.

The present invention has for its object various improvements in drum brakes which floating jaws, of the kind in which, between the oppositely-facing extremities of two brake jaws mounted floating with respect to the drum, there are interposed, on the one hand an operating cylinder in which slide two pistons, each bearing against one of the said jaws through the intermediary of a coupling rod, and on the other hand an automatic device for taking-up play due to wear of the friction linings carried by the brake jaws, the said device being diametrically opposite to the operatingcylinder with respect to the axis of the drum.

In accordance with certain arrangements currently employed in brakes of this type, the automatic device for taking-up play due to wear is of the unidirectional type with step-by-step operation, and is actuated by an operating member responsive to the movement of the jaws. This operating member is generally constituted by levers articulated on a jaw, by rods, cables or by any other similar members.

The device for taking-up play is actuated during the movement of the jaws, preferably during braking on reverse running, either during the movement of the jaws during braking, the re-setting of the operating member being effected during the return movement of the jaws to their initial position, or during the movement of return of the jaws to their initial position, the re-setting of the operating member being effected during the movement of the jaws during the course of braking.

While arrangements of this kind are quite suitable when at least one of the brake jaws is articulated on a fixed point, difficulties appear in a brake of the kind referred to, due to the fact that the two floating jaws of this brake must, in the absence of braking, take-up an indifferent position of equilibrium, without being urged towards the drum by any component of force.

In accordance with one of the improvements according to the invention, relating to a particularly simple, effective and robust construction of such an operating member, this latter is a single lever carried by one of the brake jaws with an articulated coupling connected to the operating cylinder by an abutment rod parallel to 3,425,521 Patented Feb. 4, 1969 the coupling rod associated with the brake jaw considered, subjected to the action of elastic restoring means and provided with an elbowed extension in engagement with the device for taking-up play, the said abutment rod being supported against the said lever at a point of the lever remote from a plane perpendicular to the axis of the drum and passing through the said articulated coupling.

The abutment rod of the operating lever being parallel to the coupling rod associated with the brake jaw which carries this lever, the elastic means which act on this latter are not capable of producing on the brake jaws components of force which urge them in a direction in which they would return to rest and come into untimely frictional contact with the drum.

In addition, this abutment rod is preferably arranged with respect to the axis of the drum, at the same distance from the centre as the associated coupling rod. By virtue of this arrangement, which furthermore enables the abutment rod to be as close as possible to the operating cylinder, the actuating lever can conveniently follow the movement of the associated brake jaw as and when it becomes Worn. Thus, the actuating lever always operates the device for taking-up play under the same conditions, irrespective of the amount of wear of the brake linings.

According to one form of construction, the abutment rod of the actuating lever passes with play through an opening in this latter and is provided at its extremity with abutment means which can be adjusted longitudinally along the said rod.

Furthermore, in brakes of this kind referred to, the step of the automatic device for taking-up play due to wear, the dimensions of the operating member, the positions of the various articulations of this latter, and the positions of the various elements, are a function of the actual geometry of the brake and of the forces to which these various elements are subjected. Thus, the change of any dimension, for example a modification of the distance from the centre of the operating cylinder, or of the arrangement of the device for taking-up play, makes it necessary to utilize an actuating member of different dimensions, and this operation is frequently only possible with difficulty, the more so since the movement of the operating member necessary to cause the device for taking-up play to move forward by one step involves a minimum approach travel of the jaws which is not always compatible with the requirements of volume of the hydraulic circuit associated with the operating cylinder, especially in the case where the device for taking-up play is actuated during the movement of braking.

In accordance with another improvement according to the invention which has the particular advantage of permitting the possible travel of the operating member to be increased, while retaining the same device for automatically taking-up play due to wear, one of the pistons of the operating cylinder, known as the primary piston, being provided with a shoulder intended to come into contact with the corresponding extremity of the said cylinder, elastic means, such as Belleville washers for example, coil springs, elastic rings, etc., are interposed between the said shoulder and the said extremity of the cylinder. This arrangement renders possible an additional displacement of all the parts of the brake under a suflicient force generated by the braking reaction following the outward movement of the other piston, known as the secondary piston, during a braking action, and thus enables the travel of the operating member to be increased. This arrangement has the additional advantage that these elastic means taken separately as such, can play the part of a shock-absorber and thus reduce or even eliminate the shocks of the primary piston on the cylinder during a braking operation on reverse running.

In accordance with a further improvement of the invention and concerning a brake of the kind in which the cylinder has a double supply circuit and comprises a primary chamber defined at least in part by the primary piston, a secondary chamber defined at least in part by the secondary piston, a so-called centering spring being arranged in the secondary chamber, there is provided a clearance at rest between the two said pistons, so that these latter can only come into contact with each other against the action of the said centering spring.

In the case of excessive heating of the drum having caused a thermal expansion of the drum sufiicient to cause the forward movement by one or more steps of the device for taking-up play, this arrangement makes it possible to prevent the wheel from becoming locked when the drum cools; such a locking effect is replaced by a limited increase in the tension of the centering spring.

Other characteristic features and advantages of the invention will furthermore be brought out in the de scription which follows below of forms of construction given solely by way of non-limitative examples, reference being made to the accompanying drawings, in which:

FIG. 1 is a view in elevation of a drum brake in accordance with the invention;

FIG. 2 is a view in cross-section of this brake taken along the line IIII of FIG. 1;

FIG. 3 is a further view in cross-section of this brake taken along the line III-III of FIG. 1;

FIG. 4 is a view on a larger scale in partial crosssection of another type of brake, the said section passing through the axis of the operating cylinder;

FIG. 5 is similar to FIG. 4 and and relates to an alternative form of construction;

FIGS. 6 and 7 are views in partial cross-section and relate to two further alternative forms of construction.

In FIG. 1 there is shown a drum brake of the kind in which two brake jaws 10A, 10B are mounted floating inside a drum 11 which has only been shown diagrammatically in chain-dotted lines in this figure. Each jaw 10A, 10B is formed by a wall 12 constituting a section of cylinder which carries externally a friction lining 13, and by a central rib 13 perpendicular to the shaft 15 of the drum 11.

The jaws 10A and 10B are subjected on the one hand to an operating device 16 arranged between two of the facing extremities of the jaws, and on the other hand to a device 17, arranged between the two other facing extremities of the jaws, diametrically opposite to those preceding with respect to the shaft 15 of the drum, this device 17 having the object of effecting automatic takeup of play due to wear of the friction linings 13.

The operating device 16 comprises a fixed cylinder 18 in which slides a primary piston and a secondary piston (not shown). In each piston there is formed externally a recess in which is supported a coupling rod 23A, 23B respectively, mounted between this piston and the corresponding brake jaw with a notch-type support of the usual kind.

The device 17 for taking-up play is of the type comprising a notched wheel 28 keyed on a threaded shaft 29- which bears against one of the brake jaws, the jaw 10B, and which is engaged by screwing into a body 130 bearing against the other brake jaw, the jaw 10 A. The wheel 28 is subjected to to the action of an operating member responsive for the movements of the brake jaws, this operating member according to the invention being a flat lever 30 slightly inclined with respect to the central rib 14 of the jaw 10B and mounted on this rib by means of two notch couplings 31 and 32 with sufficient play to permit, on the one hand the mounting of the lever 30 on the rib 14, and on the other hand rotation of the lever 30 about the alignment axis of the said notch couplings 31 and 32. The inclination of the lever 30 on the rib 14 is made sufficient for it to be always in the same direction irrespective of the movements of rotation of the lever 30 about the notches 31, 32, thus enabling a modification of the support of the lever 30 to be avoided at the level of these notches.

The operating lever 30 is coupled to the fixed cylinder 18 by a rod 33 parallel to the coupling rod 23B associated with the brake jaw 10B. The rod 33 is engaged with play in an opening 34 formed in the lever 30 at a point located outside the plane passing through the axis of the operating cylinder 18 and through the axis of the device 17 for taking-up wear, and the extremity of the rod 33 comprises a head 55 intended to abut against the lever 30.

At its lower extremity, the operating lever 30 comprises an elbowed extension 38 intended to come into engagement with the notched wheel 28 so that the lever 30 rests vertically on the wheel 28 and not on the notches of the associated jaw, as shown in FIG. 3.

It will be noted that the lever 30 is constituted in a single piece formed for example in the method of construction shown, by suitably cutting-out and bending a flat sheet. A lever of this kind in a single piece could of course be produced by suitably fixing together two or more parts.

The assembly is completed by the usual restoring springs 40 and 41, the spring 41 according to the invention being coupled to the operating lever 30 so as to return this latter and the brake jaws, and by a spring 42 coupled between the brake jaw 10B and the operating lever 30 for the maintenance of the extension 38 of this latter in engagement with one of the notches of the notched wheel 38.

During a braking action in forward running or in reverse running, the secondary piston pushes the rod 238 out of the cylinder 18, which causes a displacement of the jaw 10B, during the course of this displacement the operating lever 30, supported against its abutment 55, pivots about the notch couplings 31 and 32. If the wear of the friction linings is suflicient, this pivotal movement causes the setting of the operating lever 30, that is to say the engagement of the extension 38 of this lever in another notch of the wheel 28.

When the braking action has ceased, the spring 41 brings back the operating lever 30 to its position of rest, together with the brake jaws, in the course of which movement the extension 38 of the lever 30 causes the wheel 28 to rotate in a direction which ensures the movement of the shaft 29 out of the body 130, and in consequence produces a slight relative movement apart of the brake jaws which is intended to compensate for wear of the friction linings.

The arrangement of the rod 33 parallel to the rod 23B makes it possible to prevent any stray component of force from acting on the brake jaw 10B in a direction in which it would come into untimely frictional contact against the drum in the absence of any braking action.

It will be noted that the rod 33 is thus arranged as close as possible to the operating cylinder 18, at the same distance from the centre as the rod 23B. In this way, the lever 30 can conveniently follow the general movement carried out by the brake jaw B, as and when its friction lining wears, it being known that this wear is more accentuated at the extremity of this jaw which is nearest to the operating cylinder. Thus, the lever 30 can always actuate the wheel 28 under the same conditions, irrespective of the wear of the friction lining of the jaw 10B.

It will also be noted that the spring 42 ensures a permanent contact of the extension 38 of the lever 30 with the wheel 38, which also makes it possible to ensure the locking of this latter when at rest.

FIGS. 4 and 7 relate to the application of the invention to brakes of the kind in which the secondary piston moves into the cylinder '18 during braking on forward running.

This is especially the case with brakes of the so-called self-stabilizing type, such as described in all or part of the French patents taken out by the applicants on Mar. 8, 1956 under the No. 1,146,888, Apr. 11, 1967 under the No. 71,181 as an addition to the preceding Oct. 8, 1957, under the No. 1,184,055, Nov. 4, 1958 under the No. 74,- 608 as an addition to the preceding, and Feb. 13, 1962 under the No. 1,325,643.

The operating cylinder of a brake of this kind shown in axial cross-section in FIG. 4, has a double supply circuit and comprises a primary chamber defined at least in part by the primary piston 19A, and a secondary chamber defined at least in part by the secondary chamber 19B, a spring 20 known as the centering spring, being arranged in the said secondary chamber.

As can be seen from FIG. 7, the extremity of the to 33 is threaded for co-operation with a nut 36 intended to abut against the lever 30 with the interposition of a socket 37 passing with clearance through the hole 34 in the lever 30.

The nut 36 permits, by screwing and taking into account the various unavoidable tolerances of assembly, to give the lever 30 a position, in the absence of braking, in which the active portion of the extension 38 of this leveris spaced apart from the lower extremity of the brake jaw 10B by a distance less than that corresponding to the pitch of the notches in the wheel 28.

During braking on forward running, the secondary piston 19B moves into the cylinder 18, and the jaw 10B also moves the operating lever 30', the rod 33 being then inoperative. The lever 30 moves until its extension 38 comes into abutment against the lower extremity of the jaw 10B which, by reason of the adjustment referred to below, takes place before the wheel 28 has moved forward by one notch.

By this means, the lever 30 is rendered inactive during braking on forward running.

On the other hand, during braking on reverse running, the lever 30 actuates the Wheel 28, following a process similar to that described above.

In addition, according to another improvement of the invention, which can be put into operation independently, of the arrangements previously described, a Belleville washer 27 is interposed between an annular shoulder of the primary piston 19A and the oppositely-facing extremity 26 of the cylinder 18. This washer 27 serves to damp the shocks which may arise between the primary piston 19A and the cylinder 18 during a braking action on reverse running.

It will be understood that in the case of the use of a Belleville washer of this kind in combination with the foregoing arrangements, the possible additional rotation of the brake jaws due to a possible compression of the Belleville washer 27 permits the possible travel available for the lever 30 to be increased and in consequence advantageously enables this same lever to be adapted to various types of brakes different from each other, for example by a particular dimension of construction.

In accordance with the alternative form shown in FIG. 5, the Belleville washer 27 is replaced by a shook-absorber ring 27 of rubber, having the same function as the spring washer. In addition, a clearance J between the oppositel-y-facinig shoulders 21A, 21B of the pistons 19A, 19B respectively, is provided in the position of rest.

This latter arrangement has the purpose, after excessive heating of the drum 11 has resulted in a thermal expansion of this latter sufficient to cause rotation of the wheel 28, following the process explained above, of preventing the Wheel from becoming locked after the drum has cooled. A locking action of this kind is replaced in this case by a simple limited increase in the tension of the centering spring 20.

In accordance with the alternative form of construction shown in FIG. 6, the spring 41 merely serves to return the brake jaws, and for returning the lever 30 a separate spring 50 is interposed between a lug 51 on the operating lever 30 and a cup 52 coupled by a rod 53 to the central rib 14 of the brake jaw 10B.

It 'Will of course be understood that the present invention is not limited to the forms of application and construction described and shown, but includes all alternative forms of construction and/or application, especially as regards the type of drum brake with floating jaws, the application of the invention to self-stabilizing brakes being in no way limitative.

What I claim is:

1. In a drum brake with floating jaws of the kind in which, between the oppositely-facing extremities of two brake jaws mounted floating with respect to the drum, are interposed on the one hand an operating cylinder in which slide two pistons, each bearing against one of said jaws through the intermediary of a coupling rod, and on the other hand a device for automatically taking-up play due to wear of the friction linings carried by said brake jaws, said device being diametrically opposite to the op erating cylinder with respect to the axis of the drum, in which said device for automatically taking up play due to wear is of the unidirectional type with step-by-step operation and is driven in rotation by an operating member responsive to the movements of said jaws; the improvement in which said operating member is in the form of a lever, an articulated coupling by which said lever is mounted on one of said brake jaws for swinging movement transverse to the axis of said drum, an abutment rod by which said lever is coupled to the operating cylinder, said abutment rod being parallel to the coupling rod associated with the brake jaw on which the operating lever is mounted, elastic restoring means for urging the lever against the abutment rod, the lever having an elbowed extension in engagement with said device for taking-up play and said abutment rod bearing against said lever at a point on the lever spaced apart from a plane perpendicular to the axis of said drum and passing through said articulated coupling.

2. A drum brake as claimed in claim 1, in which said abutment rod is disposed with respect to the axis of the drum at the same distance from the centre as the associated coupling rod.

3. LA drum brake as claimed in claim 1, in which said device for taking-up play comprises a notched wheel keyed on a threaded shaft bearing on one of said brake jaws and engaged by screwing in a body which bears in turn on the other brake jaw, said wheel being in engagement with said operating lever.

4. A drum brake as claimed in claim II, in which said operating lever is in the form of a plate and is arranged in such manner that the mean plane of said plate is slightly inclined to the axis of the drum.

5. A drum brake as claimed in claim 1, in which said brake jaw has a wall forming a section of cylinder intended to carry the associated friction lining fixed on a central rib perpendicular to the axis of the drum, said articulated coupling being affected by mounting with notches, with play, of the operating lever on said central rib of the associated brake jaw.

6. A drum brake as claimed in claim 1, in which said abutment rod passes with a clearance through a hole in said lever and is provided at its extremity with abut-ment means bearing on said lever.

7. A drum brake as claimed in claim 6, in which said abutment means are adjustable in position longitudinally along said abutment rod.

8. A drum brake as claimed in claim 1, in which a restoring spring is provided between the two jaws, said restoring spring being coupled on the one hand to the opcrating lever and on the other hand to that jaw which does not carry said lever and comprising the elastic restoring means of said lever.

9. A drum brake as claimed in claim 1, in which the elastic restoring means of said operating lever comprises an independent spring interposed between said lever and the associated brake jaw.

10. A drum brake as claimed in claim 1, and at least one elastic means for acting continuously on the elbowed extension of said operating lever in engagement with the device for taking-up play.

11. A drum brake as claimed in claim 1, in which there is provided an abutment of said elbowed extension of the operating lever at a distance such that, in the absence of braking, the distance which separates said abutment from the active portion of the elbowed extension of the operating lever is less than one pitch of the step-'by-step device for taking-up play.

12. A drum brake as claimed in claim 1, in which said primary piston is provided with a shoulder intended to come into contact against the corresponding extremity of the associated cylinder, and elastic means interposed between said shoulder and the extremity of said cylinder.

13. A drum brake as claimed in claim '1, in which said cylinder has a double supply circuit and comprises a primary chamber defined at least in part by a primary piston and a secondary chamber defined at least in part by a secondary piston, a centering spring disposed in said secondary chamber, a clearance being provided between the two pistons in the position of rest, whereby said pistons can only come into contact with each other against the action of said centering spring.

14. A drum brake as claimed in claim 1, in which said elastic restoring means urges away from said cylinder that portion of said lever which bears against said abutment rod.

References Cited UNITED STATES PATENTS 1,974,943 9/1934 Baits 18879.5 3,111,200 11/1963 Gores 18879.5 3,294,201 12/1966 Swift 18879.5

DUANE A. REGER, Primary Examiner.

US. Cl. X.R. 188196 

